Friction drive belts such as V-ribbed belts are typically configured to have a stacked structure of an adhesion rubber layer having a core wire embedded therein and a compression rubber layer serving as a portion that is to contact pulleys.
Patent Document 1 discloses that since stress is intensively applied to a specific part of the interface between an adhesion rubber layer and a compression rubber layer when a belt is subjected to a tensile or bending force, and such concentration of stress can cause cracks in the belt, fibrillated short fibers, which are made of aramid fibers, cotton, or silk, are contained in the adhesion rubber layer in order to reduce the difference in elastic modulus between the adhesion rubber layer and the compression rubber layer.
It is also known that stacking a back portion of a belt, which is made of a rubber composition, on the outer side of an adhesion rubber layer increases the power transmission capability of the back portion of the belt.
Patent Document 2 discloses that monofilaments having a flat transverse section are embedded in a backing rubber layer of a V-ribbed belt. Patent Document 2 describes that embedding the monofilaments in the backing rubber layer can prevent occurrence of vertical splits in ribbed rubber in grooves of V-shaped ribs.